Medical devices implanted in patients may communicate with devices external to the patients via distance telemetry, such as radio frequency telemetry. Such distance telemetry communications do not require the external device, such as a programmer, to be located in close proximity to the patient, and thus are more convenient than proximity telemetry communications. While distance telemetry provides convenience to the communication process, security and unintentional access is a concern. For example, it may be possible that multiple implanted devices are within telemetric range of an external programming device. If a device implanted in one patient receives therapeutic instructions intended for a device implanted in another patient, the consequences could be dire. By way of another example, it may be possible for unauthorized parties to eavesdrop on such distance telemetric communications or to send unauthorized communications to an implanted device. Accordingly, there is a need to provide more secure communication associated with distance telemetry with implantable medical device.